1. Field of the Invention
The present invention relates to a numerical controller, and particularly relates to a numerical controller having a machining time prediction function that takes servo control and delay of mechanical motion into consideration.
2. Description of the Related Art
In machining a workpiece using a machine tool, in general, machining accuracy deteriorates when a machining speed is increased to shorten a machining time. Conversely, machining accuracy is improved when the machining speed is decreased to prolong the machining time. For this reason, a user who machines the workpiece using the machine tool desires to “machine the workpiece with the machining time as short as possible at machining accuracy within an allowable machining error set in advance”. However, it is not easy to ascertain an extent of a machining error and an extent of a machining time with which the workpiece can be machined.
In this regard, various trials and errors have been repeated such that a machining time is attempted to be shortened while maintaining machining accuracy by performing trial machining while changing setting of a parameter, etc., or machining accuracy and a machining time are predicted by performing simulation without trial machining.
As a main conventional art related to predicting a machining time, there are Japanese Patent Application Laid-Open No. 2003-175439, Japanese Patent Application Laid-Open No. 2012-243152, Japanese Patent Application Laid-Open No. 11-028643, Japanese Patent Application Laid-Open No. 2014-038482 A, and Japanese Patent Application Laid-Open No. 2012-502270. Japanese Patent Application Laid-Open No. 2003-175439 discloses a technology for predicting an accurate machining time by accumulating a time of an auxiliary function for each auxiliary code and reflecting an average value thereof on a predicted machining time. Japanese Patent Application Laid-Open No. 2012-243152 discloses a technology for enabling more accurate prediction of a machining time and a machining error by simulating a servo operation. Japanese Patent Application Laid-Open No. 11-028643 discloses a technology for predicting a more accurate machining time than only a predicted machining time by measuring a time corresponding to actual machining during machining and adding the predicted machining time to the actual machining time. In addition, Japanese Patent Application Laid-Open No. 2014-038482 discloses a technology for enabling accurate machining time prediction in consideration of an acceleration and deceleration time and a program execution order by dividing a tool path into smaller units than a block referred to as a segment, and increasing a traveling time of the segment to use the traveling time as a machining time in consideration of processing ability of the numerical controller. Further, in a technology disclosed in Japanese Patent Application Laid-Open No. 2012-502270, a machining time is predicted by calculating delay due to acceleration and deceleration, delay due to servo control, and delay of movement of a machine.
In general, when the machine is operated, so-called machine delay such as delay due to acceleration/deceleration, delay due to servo control, delay of movement of the machine, etc. occurs due to operation delay based on a frictional force generated in each part, delay of a feedback system, operation delay caused by inertia, etc. (FIG. 4). However, in the technologies disclosed in Japanese Patent Application Laid-Open No. 2003-175439 and Japanese Patent Application Laid-Open No. 2012-243152, such machine delay is not taken into consideration, and thus there is a problem that an error occurs in a machining time prediction result. In addition, in the technology disclosed in Japanese Patent Application Laid-Open No. 11-028643, even though prediction accuracy is high near an end of machining, machine delay is not sufficiently reflected in a prediction result at an early stage of machining, and thus an error occurs in a machining time prediction result. Further, in the technologies disclosed in Japanese Patent Application Laid-Open No. 2014-038482 and Japanese Patent Application Laid-Open No. 2012-502270, even though calculating a time of machine delay is suggested, a scheme of calculating a time of a specific machine delay is not disclosed. In addition, since a characteristic of machine delay is different for each machine, even when a calculation scheme is disclosed, it is difficult to respond to all types of machine delays, and accurate prediction cannot be performed.